Metal-oxide-silicon device including nanometer scaled oxide structure to enhance light-emitting efficiency

ABSTRACT

A metal-oxide-silicon (MOS) device that at least includes a silicon-based substrate, a nanometer scaled oxide layer formed on the silicon-based substrate and a metal layer formed on the oxide layer, is disclosed. The present invention basically uses a nanometer scaled oxide structure that result in a non-uniform tunneling current to enhance light-emitting efficiency. The manufacturing steps of the MOS device according to the present invention are quite similar to those of conventional MOS device, so the MOS device according to the present invention can be integrated with the current silicon-based integrated circuit chip. Further the application fields of the silicon-based chip and material can be extended. The cost of MOS device can be reduced and its practicality can be increased.

FIELD OF THE INVENTION

The present invention relates generally to a metal-oxide-silicon deviceincluding a nanometer scaled oxide structure to enhance light-emittingefficiency, and in particular to a metal-oxide-silicon device that canemit light by way of electron excitation, and enhance light-emittingefficiency by way of a nanometer scaled oxide structure.

BACKGROUND OF THE INVENTION

In accordance with the prior art, metal-oxide-silicon (abbreviated as“MOS”) device was given out by Moll, Pfann and Garrett at 1959. However,the known MOS device has not been put to use in the application ofelectroluminescent element. MOS device was originally developed for thepurpose of voltage-controlled capacitor. In 1970s, Boyle and Smith firstput through a new concept of charge-coupling and made charge-coupleddevice (CCD) accordingly, which has become a crucial component in adigital camera. In 1980s, MOS device has been widely used as a keyelement in integrated circuits (ICs). CMOS (complementarymetal-oxide-semiconductor) transistor that is made up of an n-channelMOSFET (metal-oxide-semiconductor field-effect transistor) together witha p-channel MOSFET plays a significant role in a very-large scaledintegrated (VLSI) circuit or an ultra-large scaled integrated (ULSI)circuit. Even in the case of a solar cell, MOS device is still treatedas a high-valued component. Although MOS device plays an extremelyimportant role in microelectronic circuits, its application inlight-emitting device is not highly expected because of the indirectbandgap of silicon.

Even so, the applicant has disclosed a MOS light-emitting diode inTaiwanese Patent Publication No. 456057 filed on Jun. 17, 1999, whereinthe MOS device is capable of emitting light by way of electronexcitation and turns into a light-emitting diode. The disclosed MOSlight-emitting diode in this example is also known as “MOSLED”.

The applicant therefore contributes heaps of efforts to improve thelight-emitting efficiency of conventional MOSLED device, and finallydeveloped a MOS device including a nanometer scaled oxide structure toresult in a non-uniform current to enhance light-emitting efficiency.

SUMMARY OF THE INVENTION

An object of the present invention is the provision of a MOS deviceincluding a nanometer scaled oxide structure to enhance light-emittingefficiency, which basically uses the nanometer scaled oxide layer toresult in a non-uniform tunneling current to enhance light-emittingefficiency.

Another object of the present invention is the provision of a MOS deviceincluding a nanometer scaled oxide structure to enhance light-emittingefficiency, wherein its manufacturing steps are quite similar to thoseof conventional MOS device, so that it can be integrated with currentsilicon-based chip. It may further extend the application fields ofsilicon-based chip and material.

Another further object of the present invention is the provision of aMOS device including a nanometer scaled oxide structure to enhancelight-emitting efficiency, wherein its structure and manufacturing stepsare quite simple and its cost is inexpensive.

The other objects, features and advantages of the present invention willbecome more apparent through the following descriptions with referenceto the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of the MOS structure according to apreferred embodiment of the present invention;

FIGS. 2A and 2B show the energy band of silicon of a N-type MOSLED inthe absence of bias voltage according to a preferred embodiment of thepresent invention;

FIGS. 3A and 3B show the energy band of silicon of a one-dimensionalN-type MOSLED and a one-dimensional P-type MOSLED in which the metallayers are respectively applied with forward bias voltage and reversebias voltage according to a preferred embodiment of the presentinvention;

FIG. 4 shows a compilation of current I-V curves under forward biasaccording to a preferred embodiment of the present invention;

FIG. 5 shows the two-dimensional energy band of a N-type MOSLED in whichthe metal layer is applied with forward bias voltage according to apreferred embodiment of the present invention;

FIG. 6 illustrates the manufacturing steps of the MOSLED according to apreferred embodiment of the present invention;

FIG. 7A is a compilation of light intensity-current curve according to apreferred embodiment of the present invention; and

FIG. 7B is a compilation of light intensity-current curve that isplotted on the condition that the oxide layer does not containnano-particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention has been disclosed in public in IEEE conferenceduring Oct. 28, 2001 to Oct. 30, 2001, wherein the related dissertationis also incorporated herein for reference. The conception of the presentinvention is to remove the limitations on the application of MOSLED dueto the indirect bandgap of silicon, so as to enhance the light-emittingefficiency of MOSLED.

The fundamentals of enhancing light emitting efficiency for MOSLEDaccording to the present invention is achieved by way of tunnelingphenomena in quantum mechanic. While the thickness of oxide layer isthin at the level of nanometer range, the probability of electrontunneling within MOSLED will increase greatly. The probability ofelectron tunneling will rapidly increase with the forward bias voltage.However, the oxide layer is not a conductor, and a round bias voltagewill be applied across the oxide layer. That is, different bias voltagesare applied across the metal layer and silicon substrate, which causethe energy bandgap of silicon to bend. In the case of N-type siliconsubstrate, the energy band of silicon in the proximity of thesilicon-oxide interface will bend down under forward-biased condition. Apotential well for electron will be generated and a large number ofelectrons will be accumulated here. In the mean time, a large number ofholes will reach the potential well by way of tunneling effect.Therefore, a large number of electrons and holes can be recombined hereto generate photons. In the case of P-type silicon substrate, thefundamentals of generating photons by way of electron excitation can bededuced in a similar way.

If silicon dioxide nano-particles are deposited between the siliconsubstrate and metal layer, an oxide layer with a non-uniform thicknesscan be obtained. On the condition that a bias voltage is applied to themetal layer and silicon substrate, the potential well as mentioned abovewill not only be limited to be perpendicular to the silicon-silicondioxide interface, but also be limited to be parallel to thesilicon-silicon dioxide interface. Thus a three-dimensional potentialwell be formed, which results in a local accumulation of electrons andholes. In this manner, the light-emitting efficiency will be enhancedgreatly.

In accordance with quantum mechanics and semiconductor device physics,it is known that the oxide layer with a thickness at the level ofnanometer has the following characteristics:

1. The electrons are allowed to pass through the oxide later by way oftunneling effect, while the probability of electron tunneling willincrease rapidly with the increase of applied voltage.

2. The probability of electron tunneling will decrease with the increaseof the thickness of oxide layer.

The foregoing concept is part of physical mechanism that is known tothose familiar with MOS techniques in the field of semiconductor. Inaddition, the energy band of silicon in the proximity of silicon-oxideinterface will bend to generate a potential well for electron or hole.Consequently, a large number of electrons or holes will be accumulatedhere. The probability of recombination of electrons and holes andgeneration of photons will greatly increase. Due to the periodictermination of silicon in the proximity of its interface, therequirements of conserving momentum are reduced, and the probability ofradiative recombination will greatly increase.

In order to further illustrate the structure and the effect of MOSLED inaccordance with the present invention, it is intended to give apreferred embodiment as well as detailed descriptions in the following.

For the purpose of avoiding confusion caused by taking P-typesemiconductor and N-type semiconductor simultaneously as examples forillustration, in this preferred embodiment it is desired to use N-typesemiconductor as a way for illustration only. Referring to FIG. 1, whichshows a cross-sectional view of the MOS structure according to apreferred embodiment of the present invention. As shown, the MOSstructure including a nanometer scaled oxide structure of the presentinvention at least includes a silicon-based chip 10, a nanometer scaledoxide layer 20 formed on the silicon-based chip 10, and a metal layer 30formed on the oxide layer 20.

It is to be noted that the nanometer scaled oxide layer 20 can result ina non-uniform tunneling current and cause the energy band ofsilicon-based chip 10 to bend non-uniformly. In the presence of biasvoltage, the nanometer scaled oxide layer 20 may be formed by aninsulating material, such as nitride, but the electrons still can passthrough the oxide layer 20 by way of tunneling effect. The nanometerscaled oxide layer 20 may be formed by oxide, nitride or otherinsulating materials that allows electrons to pass therethrough by wayof tunneling effect. The nanometer scaled oxide layer 20 has a dimensionranged between 1 nm to 100 nm, and may be formed by silicon dioxidenano-particles.

The formation of the nanometer scaled oxide layer 20 may be carried outby one of the method listed in the following: non-uniform surfaceoxidization process, chemical etching, dry etching, photon bombardment,ion bombardment, electron beam development, ion beam development, X-raydevelopment, optical proximity development, atomic or penetrativeprobing that results in non-uniform oxidization. The silicon-based chip10 may be one of a P-type, N-type or undoped semiconductor.

The metal layer 30 may be formed by silver, silver paint, aluminum orIndium-Tin-Oxide (ITO) or other conducting materials, and thesilicon-based chip 10 may be replaced by other materials having anindirect bandgap, such as germanium or silicon carbide (SiC).

FIGS. 2A and 2B show the energy band of silicon in the absence of biasvoltage. Under thermal equilibrium, the energy band is curved, while nocurrent is flowing therethrough and no light is emitted. When the metallayer is applied with a positive voltage, the current is stillinfinitesimal. On the other hand, because the energy band remains tobend up and no electron is accumulated in the proximity of silicon-oxideinterface, there will not be a considerable amount of recombination ofelectrons and holes to be occurred.

While the voltage applied to the metal layer continuously increases upto a level that even up the energy band, the energy barrier that thetunneling carriers have to overcome is reduced, and thereby thetunneling current increases. While the positive applied voltagecontinuously increases, the energy band turns to bend down. It can beknown from the WKB method of quantum mechanics that the probability oftunneling is greatly increased, as shown in FIGS. 3A and 3B. Therefore,the current flowing therethrough increases rapidly (also referred to astunneling current). Referring to FIG. 4 which shows a compilation of I-Vcurves under forward bias condition according to a preferred embodimentof the present invention. It reveals that the tunneling current willincrease rapidly under flat band voltage.

While the energy band is bending down, the conduction band proximate tothe silicon-oxide interface forms a potential well for electrons, and alarge number of electrons are accumulated here. In the mean time, alarge number of electrons pass through the metal layer and reach thesilicon-oxide interface, and thus a large number of recombinations ofelectrons and holes will take place in this area. However, becausesilicon is a material having an indirect bandgap, the momentum ofelectron is not equal to that of hole. In recombination, theconservation law of momentum can not be established. Accordingly,phonons have to join in the recombination process so as to meet therequirements of momentum conservation. As a result, the probability ofrecombination of electrons and holes is insignificant under normalcondition.

However, the use of silicon dioxide nano-particles between the siliconsubstrate and the metal layer can result in an oxide layer with anon-uniform thickness, and can bring about the following effects:

1. Under forward bias condition, the voltage across a thin oxide layeris identical to that across a thick oxide layer. That is, the voltagegradient of a thin oxide layer is larger than that of a thick oxidelayer. Therefore, the level of bending of the energy band where thesilicon substrate contacts with the thin oxide layer is higher than thelevel of bending of the energy band where the silicon substrate contactswith the thick oxide layer. As shown in FIG. 5, a three-dimensionalpotential well is formed, wherein z-axis is perpendicular to thesilicon-silicon-dioxide interface and x-axis is parallel to thesilicon-silicon-dioxide interface. The energy band in the y-axisdirection is similar to that in the x-axis direction, and the y-axis ofthe three-dimensional potential well is not explicitly shown. Thethree-dimensional potential well corresponds to the location where thesilicon substrate contacts with thin oxide layer, and electrons willaccumulate in the vicinity.

2. As stated above, the probability of tunneling will increase with thedecrease of the thickness of the oxide layer. Therefore, the probabilityof tunneling for a thin oxide later is higher than that for a thickoxide layer, and a large number of tunneling holes will accumulatewithin the thin oxide layer.

The above-described effects will cause the electrons and holes to belocally accumulated in the same area. Because the dimension ofnano-particles is within 100 nm, the electrons and holes will be limitedin an area of nanometer range.

Because silicon is a material having an indirect bandgap, therecombination of electrons and holes can meet with the requirements ofmomentum conservation only when phonons take a part in the recombinationprocess. Under normal conditions, there is little probability for theelectrons, holes and phonons to get together, and thus the probabilityof recombination of electrons and holes and probability of emittinglight are very insignificant. While the electrons and holes are limitedwithin a area of nanometer range, they do not move freely. Thus thephonons are easily subject to be incorporated therein. That means thatthe original recombination that requires three kinds of particles(electrons, holes and phonons) to participate in has been changed intorecombination that requires only two kinds of particles (electron-holepairs and phonons) to participate in, and thereby the probability ofrecombination of electrons and holes are greatly increased and thelight-emitting efficiency is enhanced.

Referring to FIG. 6, which shows that the silicon dioxide nano-particlesare deposited between silicon substrate and metal layer. Themanufacturing process of the MOS device according to the presentinvention is explained as follows:

Step 100: clean the silicon substrate;

Step 200: dilute the original solution containing silicon dioxidenano-particles to decrease the concentration of nano-particles, anddeposit the nano-particles onto the silicon substrate by spin coatingprocess;

Step 300: bake the sample to remove organic solvent;

Step 400: plate a very thin aluminum film on the silicon dioxidenano-particles;

Step 500: oxidizing the thin aluminum film to form a very thin oxidelayer; and

State 600: plate the thin oxide layer with sliver or silver paint toform metal layer.

The foregoing manufacturing steps are given as a way of example only,but are not intended to be taken as a limitation on the presentinvention. The present invention may be achieved as long as thethickness of the oxide layer is non-uniform and the dimension of thefeatures within the oxide layer is at the level of nanometer.

As shown in FIG. 7A, a compilation of light intensity-current curveaccording to a preferred embodiment of the present invention isillustrated. As shown in FIG. 7B, a compilation of lightintensity-current curve that is plotted on the condition that the oxidelayer does not contain nano-particles is illustrated. It is obvious thatthe light intensity of MOS device according to the present invention isenhanced by several hundred times. As shown in FIG. 7A, for injectioncurrent of 50 mA, the emitted light intensity can reach 1.5 uW and thecorresponding external quantum efficiency is approaching 10⁻⁴. However,in FIG. 7A only the light that is emitted from the edge of silver paintis taken into count, while the other lights which are either screenedout by the silver paint or emitted from other direction are notcollected by photo detector. Therefore, if the total light is included,the actual external quantum efficiency could reach 10⁻³.

Because the manufacturing steps of the MOS device according to thepresent invention is quite similar to those of conventional MOS device,and the MOS device according to the present invention is fabricated witha silicon substrate, it can be integrated with the current silicon-basedintegrated circuit chip. This enables the silicon-based chip to beapplicable to electronic product and to serve as a high-efficiencylight-emitting element. Furthermore, the monolithic integration ofelectronic chip and light-emitting element can further extend theapplication field of the silicon-based chip and material. The structureand manufacturing steps of the MODLED device according to the presentinvention are quite simple and inexpensive, and more particularly, itcan be directly combined with the IC manufacturing industry.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by the way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A metal-oxide-silicon light emitting devicehaving enhanced light-emitting efficiency comprising: a silicon-basedsubstrate; a nanometer scaled intermediate layer formed on saidsilicon-based substrate, said intermediate layer being nanometer scaledin thickness for promoting the tunneling of electrons therethroughresponsive to a predetermined bias voltage thereacross, saidintermediate layer including at least one of an oxide and a nitridematerial; and, a metal layer formed on said intermediate layer.
 2. Themetal-oxide-silicon light emitting device according to claim 1 whereinsaid nanometer scaled intermediate layer is non-uniform in thickness toprovide a non-uniform tunneling current.
 3. The metal-oxide-siliconlight emitting device according to claim 1 wherein said nanometer scaledintermediate layer is configured to bend an energy band of saidsilicon-based chip non-uniformly in the presence of the bias voltagethereacross.
 4. The metal-oxide-silicon light emitting device accordingto claim 1 wherein said nanometer scaled intermediate layer is formed bya nanometer scaled nitride material forming an insulating layer, whichallows electrons to pass therethrough by a tunneling effect.
 5. Themetal-oxide-silicon light emitting device according to claim 1 whereinsaid nanometer scaled intermediate layer is an oxide material forming aninsulating layer, which allows electrons to pass therethrough by atunneling effect.
 6. The metal-oxide-silicon light emitting deviceaccording to claim 1 wherein said nanometer scaled intermediate layerhas a thickness dimension ranged between approximately 1 nm and 100 nm.7. The metal-oxide-silicon light emitting device according to claim 4wherein said nanometer scaled intermediate layer has a thicknessdimension ranged between approximately 1 nm and 100 nm.
 8. Themetal-oxide-silicon light emitting device according to claim 5 whereinsaid nanometer scaled intermediate layer has a thickness dimensionranged between approximately 1 nm and 100 nm.
 9. The metal-oxide-siliconlight emitting device according to claim 1 wherein said nanometer scaledintermediate layer includes a plurality of silicon dioxidenano-particles.
 10. The metal-oxide-silicon light emitting deviceaccording to claim 1 wherein said nanometer scaled intermediate layer isformed by a methods selected from the group consisting of: a non-uniformsurface oxidization process, a chemical etching process, a dry etchingprocess, a proton bombardment process, an ion bombardment process, anelectron beam lithography process, an ion beam lithography process anX-ray lithography process, an near-field lithography process, and anatomic-force and scanning tunneling probing process that results innon-uniform oxidization.
 11. The metal-oxide-silicon light emittingdevice according to claim 4 wherein said nanometer scaled intermediatelayer is formed by a method selected from the group consisting of: anon-uniform surface oxidization process, a chemical etching process, adry etching process, a proton bombardment process, an ion bombardmentprocess, an electron beam lithography process, an ion beam lithographyprocess an X-ray lithography process, a near-field lithography process,and an atomic-force and scanning tunneling probing process that resultsin non-uniform oxidization.
 12. The metal-oxide-silicon light emittingdevice according to claim 5 wherein said nanometer scaled intermediatelayer is formed by a method selected from the group consisting of: anon-uniform surface oxidization process, a chemical etching process, adry etching process, a proton bombardment process, an ion bombardmentprocess, an electron beam lithography process, an ion beam lithographyprocess, an X-ray lithography process, an near-field lithographyprocess, and an atomic-force and scanning tunneling probing process thatresults in non-uniform oxidization.
 13. The metal-oxide-silicon lightemitting device according to claim 1 wherein said silicon-basedsubstrate is of a type selected from the group consisting of: a P-type,N-type, and undoped semiconductor.
 14. The metal-oxide-silicon lightemitting device according to claim 4 wherein said silicon-basedsubstrate is of a type selected from the group consisting of: a P-type,N-type, and undoped semiconductor.
 15. The metal-oxide-silicon lightemitting device according to claim 5 wherein said silicon-basedsubstrate is of a type selected from the group consisting of: a P-type,N-type, and undoped semiconductor.
 16. The metal-oxide-silicon lightemitting device according to claim 1 wherein said metal layer isselected from the group consisting of: silver, aluminum,indium-tin-oxide and a conducting material.
 17. The metal-oxide-siliconlight emitting device according to claim 4 wherein said metal layer isselected from the group consisting of: silver, aluminum,indium-tin-oxide and a conducting material.
 18. The metal-oxide-siliconlight emitting device according to claim 5 wherein said metal layer isformed by a material selected from the group consisting of: silver,silver paint, aluminum, indium-tin-oxide and a conducting material. 19.The metal-oxide-silicon light emitting device according to claim 1wherein said silicon-based substrate includes a material having anindirect bandgap.
 20. The metal-oxide-silicon light emitting deviceaccording to claim 4 wherein said silicon-based substrate includes amaterial having an indirect bandgap.
 21. The metal-oxide-silicon lightemitting device according to claim 5 wherein said silicon-basedsubstrate includes a material having an indirect bandgap.